Method of determining a position of a feature

ABSTRACT

A method, system and program for determining a position of a feature referenced to a substrate. The method includes measuring a position of the feature, receiving an intended placement of the feature and determining an estimate of a placement error based on knowledge of a relative position of a first reference feature referenced to a first layer on a substrate with respect to a second reference feature referenced to a second layer on a substrate. The updated position may be used to position the layer of the substrate having the feature, or another layer of the substrate, or another layer of another substrate.

This application is a continuation of U.S. patent application Ser. No.16/465,161, filed May 30, 2019, which is the U.S. national phase entryof PCT patent application no. PCT/EP2017/080190, filed Nov. 23, 2017,which claims the benefit of priority of European patent application no.16206732.6, filed Dec. 23, 2016, each of the foregoing applications isincorporated herein in its entirety by reference.

FIELD

The present description relates to a method, system and program fordetermining a position of a feature referenced to a substrate andmethods, system and programs for controlling positioning of a substrate.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.,including part of, one, or several dies) on a substrate (e.g., a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. These target portions arecommonly referred to as “fields”.

In lithographic processes, it is desirable to frequently measure thestructures created forming a circuit pattern, e.g., for process controland verification. Various tools for making such measurements are known,including scanning electron microscopes, which are often used to measurecritical dimension (CD), and specialized tools to measure overlay, whichis the accuracy of alignment of two layers in an at least partiallypatterned substrate.

Various techniques can be used to measure performance of thelithographic process. This in turn allows sophisticated processcorrections to be included in the control of the operations performed bythe lithographic apparatus. For example, a feedback system as describedbelow is generally known for making corrections to the positioning ofthe substrates in the system by measuring the positioning error betweentwo different layers of the substrate. The positioning error between thetwo different layers of the substrate is called the overlay error.

Before exposure of a substrate, the substrate is aligned. The goal ofthe alignment is to determine, for each substrate, the field centres andlocal distortions, to limit overlay error between layers of thesubstrate. This is accomplished by measuring alignment marks that areprinted on at least one layer of the substrate. The difference betweenthe expected and measured location of the alignment marks is used as theinput for the alignment model. The alignment model (which may be basedon a linear or higher order alignment) gives an output comprisingparameters used for optimizing the position of the substrate duringsubsequent exposure of the substrate.

To further control the errors in positioning, a feedback system is usedoften called an automated process control (APC) system. The APC systemmeasures the overlay error for a number of substrates and determinescorrections required to reduce the overlay error. These corrections arethen used as input for future exposures. The APC system typicallyincludes high-order corrections per exposure. The APC system is intendedto correct slowly changing overlay errors as overlay error measurementis done only on a per lot basis. The APC system is intended to correctfor varying effects from layer to layer and from lot to lot.

These corrections typically correct for deformation of the substrate dueto, for example, process variations, clamping variations and/ortemperature variations. These effects can vary significantly persubstrate and the process of using the lot based APC control for theoverlay error still results in undesirable errors in the positioning ofthe substrate.

Furthermore, variations can be introduced due to temperature changes ina projection system of lithographic apparatus. The temperature changescan affect the illumination conditions which affects different marks indifferent ways. Although the APC control attempts to account for thesevariations, there are still undesirable errors due to temperaturechanges across the projection system.

SUMMARY

An embodiment of the present invention has the aim of improvingdetermining the position of a feature referenced to a substrate andimproving controlling positioning of a substrate.

According to an aspect of the invention, there is provided a method fordetermining a position of a feature referenced to a substrate, themethod comprises: obtaining a measured position of the feature, whereinthe feature is configured to enable positioning of the substrate;receiving an intended placement of the feature; determining an estimateof a placement error, wherein the placement error is the differencebetween the intended placement and an actual placement of the feature,based on knowledge of a relative position of a first reference featurereferenced to a first layer with respect to a second reference featurereferenced to a second layer, wherein the first layer and the secondlayer are on a substrate; and determining an updated position for thefeature using the estimate of the placement error and the measuredposition of the feature.

According to another aspect of the invention, there is provided a systemcomprising a processor configured to determine a position of a featurereferenced to a substrate, the processor configured to: measure aposition of the feature, wherein the feature is configured to enablepositioning of the substrate; receive an intended placement of thefeature; determine an estimate of a placement error, wherein theplacement error is the difference between the intended placement and anactual placement of the feature, based on knowledge of a relativeposition of a first reference feature referenced to a first layer withrespect to a second reference feature referenced to a second layer,wherein the first layer and the second layer are on a substrate; anddetermine an updated position for the feature using the estimate of theplacement error and the measured position of the feature.

According to another aspect of the invention, there is provided aprogram for controlling determining a position of a feature referencedto a substrate, the program comprises instructions for carrying out thesteps of: measuring a position of the feature, wherein the feature isconfigured to enable positioning of the substrate; receiving an intendedplacement of the feature; determining an estimate of a placement error,wherein the placement error is the difference between the intendedplacement and an actual placement of the feature, based on knowledge ofa relative position of a first reference feature referenced to a firstlayer with respect to a second reference feature referenced to a secondlayer, wherein the first layer and the second layer are on a substrate;and determining an updated position for the feature using the estimateof the placement error and the measured position of the feature.

According to another aspect of the invention, there is provided a methodfor controlling positioning of a substrate, comprising: providing asubstrate with a first mark and a second mark on one layer of thesubstrate, wherein the first mark is different from the second mark;determining a relative shift of the first mark with respect to thesecond mark; and controlling positioning of the one layer of thesubstrate, a further layer of the substrate or a layer of a furthersubstrate based on the determined relative shift.

According to another aspect of the invention, there is provided a methodfor controlling positioning of a substrate, comprising: providing asubstrate with a first mark on a first layer and a second mark on asecond layer of the substrate, the second mark comprising at least onefirst portion and at least one second portion; determining the positionof the first mark; determining a relative shift of the at least onefirst portion with respect to the at least one second portion; andcontrolling positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate based on the determinedposition and the determined relative shift. According to another aspectof the invention, there is provided a system comprising a processorconfigured to control positioning of a substrate, the processor beingconfigured to: determine a relative shift of a first mark with respectto a second mark, wherein the first mark and the second mark are on onelayer of a substrate, wherein the first mark is different from thesecond mark; and control positioning of a further layer of the substrateor a layer of a further substrate using the determined relative shift.

According to another aspect of the invention, there is provided aprogram for controlling positioning of a substrate, the programcomprising instructions for carrying out the steps of: determining arelative shift of a first mark with respect to a second mark, whereinthe first mark and the second mark are on one layer of a substrate,wherein the first mark is different from the second mark; andcontrolling positioning of a further layer of the substrate or a layerof a further substrate using the determined relative shift.

According to another aspect of the invention, there is provided a systemcomprising a processor configured to control positioning of a substrate,the processor being configured to: provide a substrate with a first markon a first layer and a second mark on a second layer of the substrate,the second mark comprising at least one first portion and at least onesecond portion; determine the position of the first mark; determine arelative shift of the at least one first portion with respect to the atleast one second portion; and use the determined position and thedetermined relative shift to control positioning of the first layer or afurther layer of the substrate or any layer on a further substrate.

According to another aspect of the invention, there is provided aprogram for controlling positioning of a substrate, the programcomprising instructions for carrying out the steps of: providing asubstrate with a first mark on a first layer and a second mark on asecond layer of the substrate, the second mark comprising at least onefirst portion and at least one second portion; determining the positionof the first mark; determining a relative shift of the at least onefirst portion with respect to the at least one second portion; and usingthe determined position and the determined relative shift to controlpositioning of the first layer or a further layer of the substrate orany layer on a further substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in which:

FIG. 1 depicts a lithographic apparatus together with other apparatusesforming a production facility for semiconductor devices, as an exampleof a system in which an embodiment of the invention may be used;

FIG. 2 is a flowchart of a method of determining and using an updatedposition of a feature of a substrate;

FIG. 3 is a flowchart of a method of determining and using an updatedposition of a feature of a substrate;

FIG. 4A illustrates the position of a first mark and a second mark whenthere is no projection system induced error and FIG. 4B illustrates theposition of the first mark and the second mark when a projection systeminduced error has caused a shift of the second mark;

FIG. 5 illustrates an example of the first and second mark; and

FIG. 6 is a flowchart of a method of controlling positioning of asubstrate.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Before describing embodiments of the invention in detail, it isinstructive to present an example environment in which embodiments ofthe present invention may be implemented. An embodiment of the inventioncan be applied, for example, in controlling a process step in alithographic manufacturing process. An embodiment of the invention canbe applied for example to control a lithographic apparatus, whenapplying patterns at locations across one or more substrates. Alithographic process for the manufacture of semiconductor devices willbe described to provide an exemplary context in which the method can beused. The principles of the present disclosure can be applied in otherprocesses without limitation.

FIG. 1 shows a lithographic apparatus LA at 100 as part of an industrialfacility implementing a high-volume, lithographic manufacturing process.In the present example, the manufacturing process is adapted for themanufacture of semiconductor products (integrated circuits) onsubstrates such as semiconductor wafers. The skilled person willappreciate that a wide variety of products can be manufactured byprocessing different types of substrates in variants of this process.The production of semiconductor products is used purely as an examplewhich has great commercial significance today.

Within the lithographic apparatus (or “litho tool” 100 for short), ameasurement station MEA is shown at 102 and an exposure station EXP isshown at 104. A control unit LACU is shown at 106. In this example, eachsubstrate visits the measurement station and the exposure station tohave a pattern applied. In an optical lithographic apparatus, forexample, a projection system is used to transfer a product pattern froma patterning device MA onto the substrate using conditioned radiationand a projection system. This is done by forming an image of the patternin a layer of radiation-sensitive resist material on a substrate.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, and/or for other factors such as the useof an immersion liquid or the use of a vacuum. In general the projectionsystem is referred to as the “lens” throughout this document, and theseterms are interchangeable. The patterning device MA may be a mask orreticle, which imparts a pattern to a radiation beam transmitted orreflected by the patterning device MA. Well-known modes of operationinclude a stepping mode and a scanning mode. As is well known, theprojection system may cooperate with support and positioning systems forthe substrate and the patterning device in a variety of ways to apply adesired pattern to many target portions across a substrate. Programmablepatterning devices may be used instead of reticles having a fixedpattern. The radiation for example may include electromagnetic radiationin the deep ultraviolet (DUV) or extreme ultraviolet (EUV) wavebands.The present disclosure is also applicable to other types of lithographicprocess, for example imprint lithography and direct writing lithography,for example by electron beam.

The lithographic apparatus control unit LACU controls all the movementsand measurements of various actuators and sensors, causing the apparatusto receive substrates W and reticles MA and to implement the patterningoperations. Control unit LACU also includes signal processing and dataprocessing capacity to implement desired calculations relevant to theoperation of the apparatus. In practice, control unit LACU will berealized as a system of many sub-units, each handling the real-time dataacquisition, processing and control of a subsystem or component withinthe lithographic apparatus LA.

Before the pattern is applied to a substrate at the exposure stationEXP, the substrate is processed at the measurement station MEA so thatvarious preparatory steps may be carried out. The preparatory steps mayinclude mapping the surface height of the substrate using a level sensorand measuring the position of alignment marks on the substrate using analignment sensor. The alignment marks are arranged nominally in aregular grid pattern. However, due to inaccuracies in creating the marksand also due to deformations of the substrate that occur throughout itsprocessing, the alignment marks may deviate from the ideal grid.Consequently, in addition to measuring position and orientation of thesubstrate, the alignment sensor in practice must measure in detail thepositions of many marks across the substrate area, if the apparatus isto print product features at the correct locations with very highaccuracy.

The lithographic apparatus LA may be of a so-called dual stage typewhich has two substrate tables, each with a positioning systemcontrolled by the control unit LACU. While one substrate on onesubstrate table is being exposed at the exposure station EXP, anothersubstrate can be loaded onto the other substrate table at themeasurement station MEA so that various preparatory steps may be carriedout. The measurement of alignment marks is therefore very time-consumingand the provision of two substrate tables enables a substantial increasein the throughput of the apparatus. If the position sensor is notcapable of measuring the position of the substrate table while it is atthe measurement station as well as at the exposure station, a secondposition sensor may be provided to enable the positions of the substratetable to be tracked at both stations. Alternatively, the measurementstation and exposure station can be combined. For example, it is knownto have a single substrate table, to which a measurement stage istemporarily coupled during the pre-exposure measuring phase. The presentdisclosure is not limited to either type of system.

Within the production facility, apparatus 100 forms part of a “lithocell” or “litho cluster” that contains also a coating apparatus 108 forapplying photosensitive resist and other coatings to substrates W forpatterning by the apparatus 100. At an output side of apparatus 100, abaking apparatus 110 and developing apparatus 112 are provided fordeveloping the exposed pattern into a physical resist pattern. Betweenall of these apparatuses, substrate handling systems take care ofsupporting the substrates and transferring them from one piece ofapparatus to the next. These apparatuses, which are often collectivelyreferred to as the “track”, are under the control of a track controlunit which is itself controlled by a supervisory control system SCS,which also controls the lithographic apparatus via lithographicapparatus control unit LACU. Thus, the different apparatuses can beoperated to maximize throughput and processing efficiency. Supervisorycontrol system SCS receives recipe information R which provides in greatdetail a definition of the steps to be performed to create eachpatterned substrate.

Once the pattern has been applied and developed in the litho cell,patterned substrates 120 are transferred to other processing apparatusessuch as are illustrated at 122, 124, 126. A wide range of processingsteps are implemented by various apparatuses in a typical manufacturingfacility. For the sake of example, apparatus 122 in this embodiment isan etching station, and apparatus 124 performs a post-etch annealingstep. Further physical and/or chemical processing steps are applied infurther apparatuses, 126, etc. Numerous types of operation can berequired to make a real device, such as deposition of material,modification of surface material characteristics (oxidation, doping, ionimplantation etc.), chemical-mechanical polishing (CMP), and so forth.The apparatus 126 may, in practice, represent a series of differentprocessing steps performed in one or more apparatuses.

As is well known, the manufacture of semiconductor devices involves manyrepetitions of such processing, to build up device structures withappropriate materials and patterns, layer-by-layer on the substrate.Accordingly, substrates 130 arriving at the litho cluster may be newlyprepared substrates, or they may be substrates that have been processedpreviously in this cluster or in another apparatus entirely. Similarly,depending on the required processing, substrates 132 on leavingapparatus 126 may be returned for a subsequent patterning operation inthe same litho cluster, they may be destined for patterning operationsin a different cluster, or the substrate 134 may be finished products tobe sent for dicing and packaging.

Each layer of the product structure requires a different set of processsteps, and the apparatuses 126 used at each layer may be completelydifferent in type. Further, even where the processing steps to beapplied by the apparatus 126 are nominally the same, in a largefacility, there may be several supposedly identical machines working inparallel to perform the step 126 on different substrates. Smalldifferences in set-up or faults between these machines can mean thatthey influence different substrates in different ways. Even steps thatare relatively common to each layer, such as etching (apparatus 122) maybe implemented by several etching apparatuses that are nominallyidentical but working in parallel to maximize throughput. In practice,moreover, different layers require different etch processes, for examplechemical etches, plasma etches, according to the details of the materialto be etched, and special requirements such as, for example, anisotropicetching.

The previous and/or subsequent processes may be performed in otherlithography apparatuses, as just mentioned, and may even be performed indifferent types of lithography apparatus. For example, some layers inthe device manufacturing process which are very demanding in parameterssuch as resolution and overlay may be performed in a more advancedlithography tool than other layers that are less demanding. Thereforesome layers may be exposed in an immersion type lithography tool, whileothers are exposed in a ‘dry’ tool. Some layers may be exposed in a toolworking at DUV wavelengths, while others are exposed using EUVwavelength radiation.

In order that the substrates that are exposed by the lithographicapparatus are exposed correctly and consistently, it is desirable toinspect exposed substrates to measure properties such as overlay errorsbetween subsequent layers, line thicknesses, critical dimensions (CD),etc. Accordingly a manufacturing facility in which litho cell is locatedalso includes metrology system MET which receives some or all of thesubstrates W that have been processed in the litho cell. Metrologyresults are provided directly or indirectly to the supervisory controlsystem (SCS) 138. If errors are detected, adjustments may be made toexposures of subsequent substrates, especially if the metrology can bedone soon and fast enough that other substrates of the same lot arestill to be exposed. Also, already exposed substrates may be strippedand reworked to improve yield, or discarded, thereby avoiding performingfurther processing on substrates that are known to be faulty. In a casewhere only some target portions of a substrate are faulty, furtherexposures can be performed only on those target portions which are good.

Also shown in FIG. 1 is a metrology apparatus 140 which is provided formaking measurements of parameters of the products at desired stages inthe manufacturing process. A common example of a metrology apparatus ina modern lithographic production facility is a scatterometer, forexample an angle-resolved scatterometer or a spectroscopicscatterometer, and it may be applied to measure properties of thedeveloped substrates at 120 prior to etching in the apparatus 122. Usingmetrology apparatus 140, it may be determined, for example, thatimportant performance parameters such as overlay or critical dimension(CD) do not meet specified accuracy requirements in the developedresist. Prior to the etching step, the opportunity exists to strip thedeveloped resist and reprocess the substrates 120 through the lithocluster. As is also well known, the metrology results 142 from themetrology apparatus 140 can be used to maintain accurate performance ofthe patterning operations in the litho cluster, by supervisory controlsystem SCS and/or control unit LACU 106 making small adjustments overtime, thereby minimizing the risk of products being madeout-of-specification, and requiring re-work. Of course, metrologyapparatus 140 and/or other metrology apparatuses (not shown) can beapplied to measure properties of the processed substrates 132, 134, andincoming substrates 130.

In the example of a lithographic manufacturing process, the substratesare semiconductor wafers or other substrates to which patterns are to beapplied in a patterning step, and structures formed by physical andchemical process steps.

In a first embodiment, at least one feature 160 may be provided on asurface of a substrate 120, 132, 132, 134 to enable positioning of thesubstrate. The feature 160 may be a specific feature intended foralignment, or any other feature which may be measured to allow thesubstrate to be aligned, e.g. before exposure. The positioning of thesubstrate may be carried out using the feature 160. The positioningincludes moving the substrate in a variety of ways, including moving thesubstrate large distances, and/or making very small adjustments to theposition of the substrate. A feature 160 is shown on substrate 130 ofFIG. 1 but may equally be found on the other substrates depicted inFIG. 1. The feature 160 may be used to align a layer of a substrate to aprevious layer (or layers) of the substrate which have already beenexposed. The feature 160 is shown as a single feature on the surface ofthe substrate, but it will be understood that the feature 160 may bepart of a grid pattern and/or there may be multiple features 160 on anysingle substrate layer. The location of the feature 160 is measured toensure that the substrate is positioned in the correct location whenexposure of the substrate 130 is carried out. As already described, anyerrors in the positioning of the substrate 130 may lead to overlayerrors potentially causing yield loss of the lithographic process. Asdescribed above, known methods for reducing overlay errors are known andsystems such as metrology system 140 and supervisory control system SCSmay already be in place to minimize overlay error.

Although the feature 160 is placed on the substrate as accurately aspossible, during exposure of the feature 160 there will normally be anerror in the placement of the feature 160. This can be referred to asthe placement error. The placement error is the difference between anintended placement of the feature 160 and an actual placement of thefeature 160. This means that the feature 160 is not printed exactly atthe desired location. Thus, when using the feature 160 to position asubstrate 130 and aligning a subsequent layer of the substrate (or alayer of a further substrate), the layer will not be at the exactposition where it is expected. Thus, any resulting position correctionsbased on the alignment measurements will contain the placement error.

The placement error may be determined in different ways. For example,lens (i.e. projection system) and/or patterning device MA distortionscan cause an overlay error having a certain fingerprint across a field(intrafield fingerprint). An overlay fingerprint is the overlay erroracross the fields of the substrate. The overlay fingerprint may varyacross the fields and/or substrates because it depends on the state ofthe substrate 130, projection system and/or patterning device MA whichwill typically change during exposure of substrates 130. The overlayfingerprint may change during exposure due to the (non-uniform)temperature increases of the substrate 130, patterning device MA and/orthe projection system. These distortions within the field are typicallyhigh-order, meaning that the centre of the field is not necessarilydisplaced, but the shape of the field may be distorted. Depending onwhere the intended placement of the feature 160 is on the substrate 130,this will mean there is a placement error which varies per lot ofsubstrates, per substrate, per layer and even per field of thesubstrate.

An error in the placement of a feature used to align layers of asubstrate can lead to overlay error. An error in the placement meansthat there is a difference between the intended location of the featuresused to position the layers, and the actual location of the featuresused to position the layers. The error in the placement of thesefeatures can lead to each of the layers being positioned in slightlyincorrect location for exposure, thus leading to overlay error. Theautomated process control (APC) system will try to account for thiserror as it will control part of the static and drifting part of theoverlay error. However, the APC system may not be able to controloverlay error variations between substrates. When overlay is criticalbetween two layers of a substrate, and those layers align to alignmentmarkers in different layers, or use different alignment models, this canresult in increased overlay variation, i.e. overlay errors. This willreduce the yield of substrates produced by the lithographic apparatus100. The effect of the placement error could possibly cancel out withoutaffecting overlay if the layers are aligned to alignment markers in thesame layers, using the same alignment model and settings of the systemmeasuring the position of the alignment markers (e.g. wavelength ofradiation used to measure and the order wherein the markers aremeasured). However, this is not always possible or desirable and imposesunrealistic physical constraints. The method described in theembodiments has fewer constraints and thus increase design freedom.

A variation in intrafield distortions and/or translation and/orrotations of the field during placement of the feature 160 results invariation during exposure of layers of the substrate which are alignedto that feature 160. When the position of the feature 160 is measured,the displacement of the feature may be interpreted as an overlay errorand thus, the field centres will be erroneously “corrected” based on atranslation error. Thus the placement error may cause an incorrect“correction” which affects alignment of the substrate which contributesto overlay error. Presently known systems do not adequately account forthe placement error.

In an embodiment, a method is provided for determining a position of afeature reference to a substrate. The method comprises measuring aposition of the feature, wherein the feature is configured to enablepositioning of the substrate. The method further comprises receiving anintended placement of the feature and determining an estimate of aplacement error. The placement error is the difference between theintended placement of the feature and an actual placement of thefeature. The placement error can be determined based on knowledge of arelative position of the first reference feature reference to a firstlayer with respect to a second reference feature reference to a secondlayer, wherein the first layer and the second layer are on a substrate.The method further comprises determining an updated position for thefeature using the estimate of the placement error and the measuredposition of the feature. The feature 160 being referenced to a substrate130 may mean that the feature is on a substrate 130, e.g. located on alayer of a substrate 130. The first reference feature and the secondreference feature being referenced to a first layer and second layerrespectively may mean that the first reference feature is on the firstlayer and the second reference feature is on the second layer.

By using both the measured position of the feature and determining anestimate of the placement error, a more accurate position of the feature(i.e. the updated position) can be determined. As described, despite theabove described known systems for correcting and reducing positioningerrors, there is a further problem that errors can be introduced whenthe feature is formed on the substrate. Using the method described aboveallows the system to account for the error in forming the feature on thesubstrate (placement error) which is later used to position thesubstrate. This is particularly beneficial as it can be used as part ofa feedforward and/or feedback system to more accurately position furtherlayers of the substrate and/or further substrates respectively. Theupdated position may be used for controlling a position of a substrate.This may be particularly useful for example for a step of patterning thesubstrate. For example, this could be used in a manufacturing process,such as a lithographic manufacturing process, of the type described inrelation to FIG. 1.

The method allows for the error in placing the feature 160 on thesubstrate 130 to be accounted for. The feature may be provided on alayer of any of the substrate 120, 130, 132, 134 shown in FIG. 1. Themethod allows the error to be determined as part of a feedback loop orfeedforward loop for positioning the layer of the substrate 130comprising the feature 160, and/or further layers of the same substrate130 and/or a layer of a further substrate 130. The feedback loop may usethe updated position for determining an updated position for furthersubstrates. The feedforward loop may use the updated position forexposing further layers on the same substrate, i.e. the substratecomprising the first reference feature and second reference feature.Thus, the updated position may be used as part of a feedback and/orfeedforward loop. The method is beneficial even for a single layer ofthe substrate 130 comprising the feature 160 because the substrate 130is more accurately positioned for exposing the layer comprising thefeature 160. For each feature 160, there might be a correspondingcorrection for the placement error of the feature 160.

The updated position can be used as an input for the alignment modeldescribed above. In other words, when the position of a feature 160 ismeasured, the updated position can be used as the input for thealignment model rather than the measured position of the feature 160. Inthis way, the placement error is accounted for. Using the updatedposition means that the placement error does not impact the alignmentmodelling and alignment corrections during exposure of the layer of thesubstrate 130 and also during exposure of further layers of thesubstrate 130 and/or further substrate(s). Thus, the method may be afeedforward method which uses the updated position for determiningplacement of further layers and/or substrates.

The method is useful for determining the updated position of the featurewhich can be used in various ways is herein described. Most simply, theupdated position of the feature 160 may be used to position a substrate130 on the basis of the updated position of the feature 160. Thesubstrate 130 may be a substrate 130 comprising the first layer and thesecond layer. The feature 160 may be positioned on the first layer orthe second layer. Thus, the substrate 130 comprising the feature 160 onthe first layer or the second layer, for example, may be positioned toalign the first layer or the second layer of the substrate 130respectively as desired. The method may further comprise exposing thefirst layer of the substrate 130 to conditioned radiation. This meansthat the first layer can be more accurately positioned to take intoaccount the placement error of the feature 160 used to align thesubstrate 130.

Alternatively, the feature 160 may be located on another layer of thesubstrate 130 comprising the first layer and/or the second layer, i.e.the feature 160 may be on the same substrate 130 as the first referencefeature and the second reference feature but on a different layer. Thus,the method may be used to position a further layer on the same substratebased on the placement error calculated for a feature 160 on a previouslayer. Alternatively, the feature 160 may be on a layer of a differentsubstrate i.e. the feature 160 may be on a further substrate for whichno measurement of the first and second reference feature is performed.Thus, the method may be used to position a further substrate based onthe placement error calculated on a previous substrate. In other words,the position of the feature may be measured on a substrate differentfrom the substrate associated with the determined estimate of theplacement error. Thus, the error estimated for one substrate can be usedto update a position of a feature 160 on another substrate.

The feature 160 may be on the first or the second layer of the furthersubstrate. Thus, the feature 160 may be placed on an equivalent layer tothe first layer or the second layer, but on a different substrate. Forexample, the first layer may in fact be a fourth layer to be exposed onthe substrate and thus, the first reference feature may be placed on thefourth layer of a substrate and the feature may be placed on the fourthlayer of another substrate. Alternatively, this may apply to the secondlayer rather than the first layer. It will be understood that theexample of the fourth layer could be replaced with any layer, includingthe first, second, third and so on.

The estimate of the placement error may be applied to selected featureson selected layers and/or substrates. Thus, it is possible to preselectthe features to which the placement error is applied. E.g. the updatedposition and/or estimate of the placement error could be applied duringexposure of all layers of all substrates in one lot, or even severallots.

As described above, the method for determining the updated position ofthe feature 160 may be particularly useful because it can be used in afeedforward or feedback system to determine positioning of furtherlayers and/or further substrates. This means that the placement errorfor one feature 160 (or for several features on one layer of a substrate130) may be used to more accurately position further layers on thesubstrate and/or substrates. This is beneficial because it is notnecessary to determine the placement error for each layer or even foreach substrate. Furthermore, once the placement error has beendetermined, this can be used for further alignments even after the layercomprising the feature 160 has been exposed. Advantageously, this meansthat measurements to determine the placement error may not be requiredon further layers and/or substrates. Reducing the number of measurementsreduces the time taken to produce semiconductor devices (i.e. fullyprocessed substrates) which is preferable. In general, the placementerror might be used for determining the placement error of furtherfeatures, even if further measurements or models are used, and can stillbe beneficial in reducing the number of measurements and/or amount ofmodelling required to determine further placement errors/updatedpositions.

The estimate of the placement error may be determined in variousdifferent ways. As already described, the estimate is based on aknowledge of a relative position of a first reference feature referencedto a first layer on a substrate with respect to a second referencefeature referenced to a second layer of the substrate. In other words,the placement error is calculated using a feature from two differentlayers of a substrate. As indicated above, the first layer and thesecond layer may be different from the layer on which the feature 160 islocated. The first layer is a different layer than the second layer suchthat the overlay can be determined between the first layer and thesecond layer. The first layer and the second layer may be adjacent toeach other, or may have one or more layers between them.

The first reference feature, the second reference feature and/or thefeature 160 may be a grating. The features may otherwise be referred toas marks. The first reference feature and the second reference featuremay be the same type of feature as each other. The first referencefeature and the second reference feature may not be of the same type asthe feature 160 for which the placement error is estimated. For example,the first reference feature and the second reference feature may not beused, or capable of being used, to align the substrate 130. The firstreference feature and/or the second reference feature may be a featureused to measure overlay, e.g. the first reference feature and the secondfeature may be gratings, optionally, overlay marks or optionally productfeatures usable to determine an overlay error. The first referencefeature and/or second reference feature may be overlay marks configuredto provide overlay feedback to the APC system. Additionally oralternatively, the feature 160 may be a grating, e.g. an alignment mark.

The method may comprise measuring the first reference feature and thesecond reference feature to determine an overlay error between the firstlayer and the second layer. Thus, the method may comprise directlymeasuring the first reference feature and the second reference featureto determine the placement error. The first reference feature and thesecond reference feature may be used to determine the overlay errorbetween the first layer and the second layer. Thus, the overlay errormay effectively be measured at the location of the first referencefeature and the second reference feature. This could be done for exampleby the APC system described above. For example, results 146 relating tothe measurements of the first reference feature and the second referencefeature may be sent from the metrology apparatus 140 to the APC system.The method may use the measured overlay error to determine the estimateof the placement error. For example, the estimate of the placement errormay be the same as the measured overlay error i.e. the estimate of theposition error and the overlay error may be one-to-one. Alternatively,the estimate of the placement error may be a function of the measuredoverlay error, or may comprise the measured overlay error. Processingsteps may be required to determine the placement error based on theoverlay error. The overlay error may not be equal to the placementerror, for example, due to different sensitivities of the feature 160and the reference feature regarding variations in process conditions andprojection system aberrations.

An exemplary implementation of a method in accordance with an embodimentis depicted in FIG. 2. In S10 the position of the feature 160 ismeasured. This step could be carried out before, after or at the sametime as step S11. In S11, the first reference feature and the secondreference feature are measured as described above. The measured firstreference feature and second reference feature may be used to determinethe estimate of the placement error in S12. In S13, the measuredposition of the feature from S10 and the estimate of the placement errorfrom S12 may be used to calculate an updated position of the feature. Aspreviously described, the feature may be on one of the first layer orthe second layer, the feature may be on another layer of the substratecomprising the first layer and the second layer (i.e. a further layer ofthe same substrate), or the feature may be on a layer of a substrate notcomprising the first layer and the second layer (i.e. a layer of afurther substrate). Thus, the updated position of the feature 160 can beused to position any of the layers comprising the feature 160 in S14.

Alternatively, the method may further comprise modelling an overlayerror between the first layer and the second layer and determining thefirst and second feature using the modelled overlay error. The methodmay comprise using an overlay model to determine the overlay erroracross at least a part of the substrate 130. The modelled overlay erroracross the substrate 130 may be used to extract the modelled position ofthe first feature and the second feature. The overlay error may bemodelled in various different ways. For example, the method may comprisereceiving context information and/or lithographic apparatus information,and using the context information and/or lithographic apparatusinformation to model the overlay error. The context information and/orlithographic apparatus information relates to measured and/or modelleddeformation of at least one of the substrate, a mask and/or theprojection system. The context information and/or lithographic apparatusinformation may include results 146 of measurements from the metrologysystem 140, and/or from the lithographic apparatus LA 100. Modelling theoverlay error may comprise using a predetermined value. This could bebased, for example, on previous overlay data, on average overlay errorsfor multiple substrates or lots of substrates or average overlay errorsbetween particular layers of substrate.

The method may use the modelled overlay error to determine the estimateof the placement error. Measurements may be taken from convenientmeasurement location(s) on the substrate 120. Modelling the overlay todetermine the position of the first reference feature and the secondfeature has the further advantage that the location of the firstreference feature and the second reference feature are not limited tobeing near the feature 160 and the first reference feature and secondreference feature may be located elsewhere away from the feature 160.The method may use the modelled overlay error to determine the estimateof the placement error. For example, the estimate of the placement errormay be the same as the modelled overlay error, i.e. the estimate of theposition error and the overlay error may be one-to-one. Alternatively,the estimate of placement error may be a function of the modelledoverlay error, or may comprise the modelled overlay error. Processingsteps may be required to determine the placement error based on theoverlay error.

An exemplary implementation of a method in accordance with an embodimentis depicted in FIG. 3. In S20 the position of the feature 160 ismeasured. This step could be carried out before, after or at the sametime as either of the steps in S21 or S22. In S21, context informationand/or lithographic apparatus information may be received as describedabove and this may be used to determine an overlay error in S22.Determining the overlay error may comprise calculating a model of theoverlay error between a first layer and a second layer to calculate amodelled position of a first reference feature and a position of asecond reference feature. The estimate of the placement error can thenbe determined based on the modelled positions of the first referencefeature and the second reference feature in S23. In S24, the measuredposition of the feature from S20 and the estimate of the placement errorfrom S23 can be used to calculate an updated position of the feature. Aspreviously described, the feature 160 may be on one of the first layeror the second layer, the feature 160 may be on another layer of thesubstrate comprising the first layer and the second layer (i.e. afurther layer of the same substrate), or the feature 160 may be on alayer of a substrate not comprising the first layer and the second layer(i.e. a layer of a further substrate). Thus, the updated position of thefeature 160 can be used to position any of the layers comprising thefeature in S25. It is noted that certain steps of FIG. 3, e.g. S20, S24,S25 may be carried out in the same way as the corresponding steps ofFIG. 2, e.g. S10, S13 and S14 respectively.

In further detail, for each exposed lot, only a few substrates may beselected and measured on the metrology apparatus 140 to determine theerror of overlay-targets on the substrate. The overlay-targets may bemarks or features which are similar to the first reference feature andthe second reference feature. These measurements can be input to the APCsystem to determine feedback overlay corrections for future exposures.Since only a few overlay-targets may be measured per lot, e.g. a fewhundred, an extrapolation and/or interpolation can be used to estimatethe overlay fingerprint for each field for each substrate as an inputfor the APC system. The extrapolation and/or interpolation from a fewhundred points per substrate can be done by fitting a mathematical modelover measured points. The resulting overlay fingerprint can be used todetermine a modelled first reference feature position and a modelledsecond reference feature position for determining the feature 160.

The overlay fingerprint may be a product of the existing APC systems.The estimate of the placement error for each feature 160 can beestimated as a function of the local overlay error:f₁(OverlayFingerprint(x,y)). This may provide a unique estimate of theplacement error for each unique overlay fingerprint. There may be aunique overlay fingerprint per substrate table (for example, because theAPC system has a particular correction loop for a particular substratetable), per lot, or per substrate depending on the overlay controlmethod which is used to determine the overlay fingerprint. As described,the simplest function would be a multiplication by 1, where the estimateof the placement error is estimated to be the same as the overlay error.More accurate estimations of f₁ can be determined by correlating overlayerrors with placement errors in either experiments or simulations. Theoverlay fingerprint can optionally be refined by using contextinformation and/or lithographic apparatus information, e.g. the resultsfrom f₁(OverlayFingerprint(x,y)) can be refined using contextinformation and/or information from the lithographic apparatus LA of 100f₂(Context information and/or lithographic apparatus information) Therefinement can, for example, result in placement error corrections persubstrate where overlay fingerprint information is only available persubstrate table and/or lot. Refinement can also result in a moreaccurate estimate of the placement error per feature 160.

To reduce the amount of measurements needed, typically the overlaycorrections can be averaged per lot or substrate table instead of persubstrate. Heating of the patterning device MA and/or a projectionsystem are known to increase errors. As described, these errors canresult in a placement error when forming a feature 160. Overlaymeasurements can be carried out on one or more substrates per lot, e.g.4 substrates per lot. To refine the results, a function f₂(Contextinformation and/or lithographic apparatus information) can be used toextrapolate the overlay fingerprint to determine what the fingerprint isexpected to be for other layers or substrates not measured. A part ofthis calculation can use context information and/or lithographicapparatus information referred to above, including parameters related topatterning device MA and/or projection system heating. This enablesdetermination of a unique estimate of the placement error for eachfeature per substrate while only 4 substrates were measured.

Alternatively, corrections can be determined per substrate, as hereindescribed. The correlation between the placement error and the overlayfingerprint may depend on the parameters included in the contextinformation and/or lithographic apparatus information. The contextinformation and/or lithographic apparatus information may include, butis not limited to, substrate table and/or projection system dynamics,and heating effects of the patterning device MA and/or the projectionsystem and/or a substrate. The context information and/or lithographicapparatus information can be measured (i.e. logged) or can be modelled.For example only, the feature 160 is likely to have a different designto the first reference feature and to the second reference feature. Thismeans that the light used to image the feature may take a different paththrough the projection system than the light used to image the firstreference feature and the second reference feature. Therefore, aprojection system aberration may have a different effect on the feature160 and the first and second reference features. The different effectscan both be measured or simulated (i.e. modelled) for severalaberrations and designs. During exposure the projection systemaberrations may be measured and this information can be combined withthe measured/modelled context information and/or lithographic apparatusinformation to refine the estimate of the placement error per feature160.

The temperature of the projection system may change whilst multiplesubstrates are exposed within a lot, i.e. in a batch. More specifically,the projection system temperature generally increases within a lot fromthe first substrate to the last substrate. In spite of arrangements tomaintain a constant projection system temperature, a small temperaturechange may occur (e.g. depending on the illumination conditions) whichis nevertheless significant for forming patterns with very smallfeatures. For example, it is know that relatively intense illuminationcan have significant heating effects especially when there are extremedipole illumination settings which may induce projection system heating.The heating of the projection lens may lead to introduction of lensaberrations, typically referred to as Zernike aberrations which areassociated with characteristic imaging effects. For example a Zernike Z7aberration is referred to as coma and typically associated with imagingshift effects; e.g. features are printed at a location which is shiftedwith respect to a desired (nominal) location.

When structures, such as overlay marks, alignment marks, and/or productfeatures have high sensitivities to Zernike aberrations, the structureswill be printed on the substrate with an unintended shift. As thetemperature of the projection system changes, the unintended shift willchange, e.g. drift, throughout the lot. The shift can be very dynamicand may depend on many parameters, which means that it is not possibleto apply process corrections (for example, using APC) to the entire lotto sufficiently account for the effects of the shift.

Various correction methods based on prediction of the lens heatingevolution may be used to reduce or minimize the effects of temperaturechanges in the projection system. However, even if these methods areused, errors relating to the temperature change across the projectionsystem (which may be referred to as projection system induced errors)may still remain (for example due to the limited accuracy of such a lensheating prediction method). When the exposed, i.e. printed, structuresare sensitive to (at least one) Zernike aberration(s), the projectionsystem induced errors may cause an image shift. Furthermore, differentstructures at different sizes have different sensitivities. In otherwords, different structures may respond to the temperature changes inthe projection system in different ways, which makes it even harder tocompensate for temperature changes. For example, different types ofstructure, e.g. product features, alignment marks and/or overlay marks,may have different sensitivities. Even different marks of the same type(i.e. which may be used for a similar purpose) for example, twoalignment marks, may have different Zernike sensitivity values. In thiscontext, the Zernike sensitivity value is an indication of thesensitivity of the mark to aberration/temperature changes in theprojection system.

The projection system induced error, e.g. translation drift, could occurwhen variation of temperature in the projection system occurs andalignment marks with a high sensitivity to aberrations are used. Thisissue may be a particular problem when certain types of feature arebeing exposed, for example, when creating memory (DRAM) because thelayers may be exposed using extreme dipole illumination conditions. Itis generally desirable to reduce the overall imaging shift error betweenlayers, e.g. the overlay error. Even relatively small potential overlaydrift of 1.5 nm for example, due to projection system induced errors areundesirable and in some cases, unacceptable.

In an embodiment, a first mark and a second mark for a single layer markare designed such that the shifts in the first mark and/or the secondmark which occur during the exposure of this single layer mark with thefirst mark and the second mark due to projection system heating areindicative of the imaging shift associated with the projection systemheating. As described below, relative shifts between the first mark andthe second mark and/or a portions of either mark may be determined for alayer of a substrate and may be used for controlling positioning of afurther layer of the substrate, e.g. the second layer. Thus, theprojection system induced errors may be corrected for in furtherlayers/substrates. This will have the benefit of reducing errors in themarks printed on the substrate. For example, this may reduce the errorin placement of the alignment mark such that the alignment mark is moreaccurately placed to the reference structure, like device pattern, whichcan reduce overlay and improve throughput. The relative shift is thedifference between the absolute distance between a first mark and asecond mark in one single layer mark and is mostly contributed by theaberration sensitivity difference between the first and second mark.

As already described, it can be beneficial to more accurately positionan alignment mark on a layer of a substrate for positioning thesubstrate. It is known that different structures, for example, analignment mark and a product feature, may be affected by variations inthe projection system in different ways. The present method takesadvantage of the difference in the effect on different types ofstructure. Thus, in a second embodiment a method for controllingpositioning of a substrate is provided. The method comprises providing asubstrate with a first mark and a second mark on one layer of thesubstrate. The first mark is different from the second mark. The methodfurther comprises determining a relative shift of the first mark withrespect to the second mark. The first mark and the second mark may be onthe same layer, and may thus, be collectively referred to as a singlelayer exposure mark. The method comprises controlling positioning of theone layer of the substrate, a further layer of the substrate or a layerof a further substrate based on the determined relative shift.Optionally, the method further comprises determining a projection systeminduced error using the determined relative shift [for example often alinear relationship exists between a Zernike aberration and thedetermined relative shift. Thus, the step of controlling position of asubstrate may be carried out using the relative shift and/or theprojection system induced error. Knowledge of the relationship allowsdetermination of the projection system induced error (aberration) basedon the determined relative shift. For example, in more detail, therelative shift can be determined by lens aberration (Zernikes) andaberration sensitivity. For example, for lithographic effects which arelinear with aberration, the sensitivity of nth order Zernike may be:

$\frac{{{displacement}\mspace{14mu}{of}\mspace{14mu}{nth}\mspace{14mu}{order}} - {{the}\mspace{14mu}{displacement}\mspace{14mu}{of}\mspace{14mu}{an}\mspace{14mu}{ideal}\mspace{14mu}{lens}}}{{nth}\mspace{14mu}{order}\mspace{14mu}{Zernike}}$

The first mark may otherwise be referred to as a first pattern or afirst mark pattern. The second mark may otherwise be referred to as asecond pattern or a second mark pattern.

FIGS. 4A and 4B depict an example cross section of the first mark andthe second mark on the one layer of the substrate. The depiction inFIGS. 4A and 4B will be described in further detail below, but it isnoted that the specific details and relative sizes shown are onlyexemplary.

The first mark is different from the second mark. This may mean that thefirst mark and the second mark have different sensitivities to anaberration in the projection system, wherein the projection system isused to expose the first mark and the second mark simultaneously. Thefirst mark and the second mark may differ in various ways to provide thedifferent sensitivities.

In the example shown in FIGS. 4A and 4B, the first mark may havemultiple first portions and the second mark may have multiple secondportions. In other words, each mark may comprise several portions, i.e.several features. It is not necessary for the first mark and the secondmark to each comprise several portions. However, this can be beneficialbecause it can be easier to detect the shift of the second mark patternwith respect to the first mark. In other words, an average relativeshift, which may be based on the relative shift of multiplecorresponding portions, may be used to more accurately determine theshift. This is particularly useful for diffraction based measurementsdescribed below. The portions which make up each mark may besubstantially uniform. Thus, the portions used for the first mark mayall be affected by a projection system aberration in the same way,and/or the portions used for the second mark may all be affected by aprojection system aberration in the same way. This means that it issimpler to predict how the projection system aberration will affect thefirst mark and/or the second mark.

In the example shown in FIGS. 4A and 4B, the wider portions are part ofthe first mark and the narrower portions are part of the second mark.The width of the portions can affect the sensitivity to aberrations inthe projection system such that the portions of the first mark havedifferent sensitivity to the portions of the second mark. Additionallyor alternatively the sensitivity of the portions may be affected bydiffracted pattern difference of exposure (DUV exposure light) andmeasurement (SMASH WA sensor), due to different patterns (segmentation).

The portions may form a grating. The first mark and the second mark areto be exposed together in the one layer of the substrate. The effect ofprojection system heating may be present on at least part of the onelayer.

Different patterns are indicated in FIGS. 4A and 4B to distinguishbetween the first mark and the second mark. The patterns shown in theseFigures are for distinguishing between the two types of mark only.

However, as indicated above, the first mark and the second mark may havedifferent sensitivities and this may be due to a variety of reasons. Anexample of the different types of portion used for the first mark andthe second mark is shown in FIG. 5. As shown, the first mark maycomprise multiple first portions and the second mark may have multiplesecond portions. As shown, at least one of the second portions maycomprise a plurality of elements. In other words, the second portion maybe segmented into elements. The pitch between the second portions may belarger than the pitch between the plurality of elements. In other words,the distance between each of the second portions may be larger than thedistance between elements of the second portions. The pitch between theplurality of elements of the second portion may be approximately thesame as the pitch of product features. Thus, the second mark may be aproduct feature or a feature having a similar response to the projectionsystem induced error as a product feature.

A first portion may comprises fewer elements than a second portion.

Furthermore, the first portion may not be segmented at all. Thus, atleast one of the first portions may comprise only a single element. Thisis indicated by the shape of the first portions shown in FIG. 5. Thusthe first mark may be an alignment mark or an overlay mark. The pitchbetween the first portions is much greater than the pitch betweenindividual elements of the second portion.

A single element of a first portion may be larger than a single elementof a second portion. This means that for example, when viewed in an X-Yplane, as is shown in FIG. 5, an element of the first portion may have agreater cross sectional area than an element of a second portion. Thus,the different sizes of the elements of the first portion and the secondportion may have different sensitivities. A single element of a firstportion may correspond in size to the plurality of elements making up asecond portion. This means that when viewed in an X-Y plane, a parameteraround the element(s) of a first portion may be of substantially similarsize to a parameter around the element(s) of a second portion. This isdepicted in FIG. 5, because although a plurality of elements may be usedto make up portions of the first and/or second mark, each of theportions of the first mark and the second mark have similar lengths andwidths overall.

Additionally, the first portions may be substantially consistent inshape and pitch, and the second portions may be substantially consistentin shape and pitch. This means that the first portions are generally thesame as each other and have a consistent distance between portions, andthe second portions are generally the same as each other and have aconsistent distance between portions. The markers may be considered tohave a grating like configuration, in other words, the markers maytypically have periodic repetition of a portion as depicted in FIGS. 4A,4B and 5. A periodic aspect of the portions may be useful in particularwhen using diffractive based measurements on the markers to determinethe relative shift between the first marker and the second marker.

Although FIG. 5 depicts that the first mark has multiple first portionsand the second mark has multiple second portions, this is for exampleonly. The first mark may have more portions than are shown in FIG. 5, ormay have fewer, or even one. The second mark may have more portions thanare shown in FIG. 5, or may have fewer, i.e. one.

The first mark and the second mark depicted in FIGS. 4A and 4B are forexample only but can be used to illustrate various features relating tothe first mark and the second mark. For example, the first mark and thesecond mark may overlap. This means that when the substrate is viewedperpendicular to the surface of the substrate, the first mark and thesecond mark appear to be overlapping at least in part. As will bedescribed, this may mean that the first portions and the second portionsare interlaced, at least for the overlapping parts of the mark. However,even when overlapping/being interlaced the individual portions of eachmark do not overlap. Thus, none of the first portions are in contactwith any of the second portions.

It is not necessary that the first mark and the second mark overlap, forexample, the first mark and the second mark may be near each other oradjacent to one another, or aligned along one edge. The relative shiftbetween the first mark and the second mark may still be determinedwithout an overlap, but having the marks overlap, i.e. by having thefirst mark extend across at least part of the second mark, may mean thatthe shift can be more accurately determined. In general, extension ofmarker, for example, a grating like marker, enables use of diffractionbased metrology, which by definition averages across the whole (at leastilluminated) part of the marker. Thus, the overlap may improve accuracyas measurement error may then also be scaled down.

The first mark and the second mark may optimally be at the same level,i.e. exposed at the same time. Ideally, the first mark and the secondmark are in the resist (right after exposure) and may be measured in theresist).

As shown in the FIGS. 4A and 4B, the first mark and the second mark maybe interlaced, or more specifically, the first portions and the secondportions may be interlaced. In other words, the first portions and thesecond portions may be alternating, as shown in FIGS. 4A and 4B. Thismay occur due to the overlapping nature of the first mark and the secondmark. The first portions and the second portions may be interlacedwithout having the first portions and the second portions overlap i.e.the first portions do not touch the second portions. In other words, thefirst mark and the second mark may overlap, but the first portions maynot contact or overlap with the second portions. This is preferablebecause it may not be possible to detect the relative shift of any ofthe second portions relative to a corresponding first portion if part ofthe first portion and the second portion are effectively in contact witheach other.

The relative shift between the first mark and the second mark isdepicted in FIGS. 4A and 4B. FIG. 4A depicts an example of how the firstmark and the second mark would be provided if the first mark and thesecond mark were exposed on the one layer of the substrate when noprojection system aberration was present. As shown in FIG. 4A, there isa distance, d, between the centre point of a portion of a first mark anda centre point of a corresponding portion of a second mark. In thisexample, the corresponding first portion and second portion are adjacentto one another. The distance, d, is the distance between thecorresponding portions of the first mark and the second mark when thereis no projection system aberration.

When there is a projection system aberration, the first mark and thesecond mark are affected (i.e. shifted). Because the first mark isdifferent from the second mark, the first mark and the second mark areaffected in different ways by the projection system aberration. Thus,the distance between the corresponding portions of the first mark andthe second mark is not the same as in FIG. 4A. As shown in FIG. 4B, thedistance between the corresponding portions of the first mark and thesecond mark when there was a projection system aberration duringexposure is s. As is clear from FIGS. 4A and 4B, distance s is not thesame as distance d. In this example, the distance between the firstportion and the corresponding second portion, s, is greater due to theprojection system aberration than the distance between the first portionand the second portion, d, when there is no projection systemaberration. It is noted that for other combinations of different marks,the distance s may be smaller than the distanced. Thus, there is arelative shift between the first mark and the second mark due to aprojection system aberration.

The relative shift depends on the state of the projection system, sothat in a case of projection system heating, drift will occur throughoutthe lot of substrates (i.e. intralot drift). Also the starting state ofthe projection system will be dependent on the usage of the projectionsystem prior to the lot. Therefore, the actual shift may varydynamically from one lot to another, or from one substrate to another.As will be described below, using the first mark and the second mark ofan embodiment of the present invention, the relative shift can bedetermined for each lot and each substrate in the lot. The determinedrelative shift can be fed forward to the next layer(s) for a substratespecific correction.

The relative shift between the first mark and the second mark can bedetermined in a variety of different ways. For example, the method maydetermine the relative shift by measuring a position of the first markand a position of the second mark after they have been exposed andcomparing the measured positions to an expected distance between thefirst mark and the second mark. Thus, the method may comprise measuringthe position of the first mark and the second mark and calculating thedistance between the first mark and the second mark. The relative shiftmay then be determined using the calculated distance between the firstmark and the second mark and an expected distance between the first markand the second mark. It is noted that the distance between the firstmark and the second mark may be the distance between a first portion anda corresponding second portion, or may be the average (e.g. mean)distance between first portions and corresponding second portions.

The first mark and the second mark may be designed in a way that allowsthe projection system heating related relative image shift between thefirst mark and the second mark to be measured using known measurementsystems after the marks are exposed. For example, the measurements maybe done using Integrated Metrology (IM) or Stand Alone Metrology (SA),typically based on diffractive measurements. Advantageously, themeasurements can be carried out on the first mark and the second mark inresist (i.e. before the substrate is processed further, e.g. subjectedto etching and/or deposition processes) which means that little or nosignificant mark degradation is to be expected. This means that theaccuracy and precision may be much higher than when measurement of anetched mark is used.

Other methods for determining the relative shift may be used. In anotherexample, the relative shift is determined using diffraction basedmeasurement. A marker comprising portions (which may form a grating),which allows the use of diffraction based measurements which are commonin the lithographic industry. A diffraction based measurement method andsystem is known and herein incorporated by reference in its entiretyfrom U.S. Pat. No. 9,134,256B2. A diffraction based measurement mayintegrate the shift error across all portions (e.g. an entire grating)and hence use determine and use of an average relative shift.Furthermore, the idea of mark measurement is known from WO2014146906 A2which is herein incorporated by reference in its entirety. WO2014146906A2 discloses measuring marks in the resist and feeding forward themeasured information to the next exposure as a substrate specificcorrection.

Optionally, a third mark, which is on a different layer to the firstmark and the second mark, may be provided. The position of the thirdmark can be determined and the position may be used with the determinedrelative shift to control positioning of the different layer of thesubstrate and/or any other layer of the substrate. The third mark may bea known, standard mark, such as an alignment mark.

An example implementation for the above described method is shown in theflow chart of FIG. 6. In step S30, a substrate with a first mark and asecond mark is provided. It is noted that this may include additionalsteps of exposing the first mark and/or the second mark as will befurther described. Additionally, this step may includeselecting/designing the structures used for the first mark and/or thesecond mark. Thus, it is possible to select a first mark and/or a secondmark which will have a desired relative shift. This may be beneficial,because a specific first mark and/or second mark may be chosen to allowthe relative shift to be more easily and/or more accurately determinedso that a more accurate estimate of the relative shift and/or projectionsystem induced error can be determined.

In a further step S31, the relative shift is determined. This may bedone using any appropriate method. Examples include those describedabove, i.e. using measurements of the position of the first and thesecond mark, or using diffractive based measurements. Optionally, therelative shift can be used to determine a projection system inducederror as shown in step S32 For example, as described above, there oftenexists a linear relationship between a Zernike aberration and thedetermined relative shift. Knowledge of the relationship allowsdetermination of the projection system induced error (aberration) basedon the determined relative shift. It is noted that more complicatedrelationships may be determined and used.

The determined relative shift and/or projection system induced error canthen be used to control positioning of one layer of the substrate, afurther layer of the substrate or a layer of a further substrate as instep S33. The determined relative shift and/or projection system inducederror can optionally be used as part of a feedback or feedforwardsystem. The determined relative shift and/or the determined projectionsystem induced error can be used in a feedback loop to controlpositioning of a layer of a further substrate and/or in a feedforwardloop to control positioning of a further layer of the same substrate.This means that the determined relative shift and/or the determinedprojection system induced error can be used to control positioning ofother layers of the substrate or layers of further substrates and theother layers/further substrates can be exposed taking into account theprojection system induced error. Step 33 includes controlling thepositioning of a substrate using feedforward and/or feedback methods.After the layer has been positioned in accordance with the above, it canbe exposed to radiation and the above described method should reduce orprevent errors due to projection system aberrations.

Advantageously, the feedback and feedforward loops means that thedetermined projection system induced error and/or the determinedrelative shift only needs to be determined for a single layer and/orsubstrate and the determined projection system induced error and/orrelative shift can then be used to correct/improve positioning offurther layers and/or substrates.

The projection system induced error may refer to any error due toprojection system aberration. This may comprise projection system driftand/or projection system heating. For example, the projection systemdrift may include intrasubstrate drift granularity (i.e. from a firstexposed field to a last exposed field). This may require densermeasurements per substrate than would otherwise be needed.Intrasubstrate correction of the projection system induced error canalso be improved by careful distribution of a number of first marks andsecond marks provided per substrate and the number of substrates perlot, ideally in addition to a good estimation model. For example,considering an example using a substrate alignment mark, aberrationimpact on a substrate alignment mark may be considered as translation-Xand translation-Y. A large number of points are not needed to calculatetranslation per substrate. Depending on intra lot drift, measurementscheme may change, as indicated below. Using this method can avoidundesirable increases in the measurement time.

The relative shift and/or the projection system induced error can bedetermined for multiple layers and/or substrates. For example, allsubstrates in the lot can be measured, or only a few of the substrates,which may optionally be evenly spread throughout the lot.

The second embodiment can be applied using the difference between anycombination of different structures, such as overlay marks, alignmentmarks and product features, etc. In the example above, the first markmay be an alignment mark. However, the first mark may alternatively bean overlay mark. The second mark may be a product feature or a featurehaving a similar response to the projection system induced error as aproduct feature. In other words, the second mark may be any structurewhich is affected by an aberration in the projection system in the sameor a similar way as a product feature would be affected. The structureused for the second mark does not have to be an actual product feature.It will be understood that the first and second terminology used inrelation to the marks is simply used for the purposes of distinguishingbetween the different marks. Thus, the first mark could be replaced withthe second mark and vice versa. The first mark and/or the second markand/or the first mark overlapped with the second mark may have the sameoverall dimension of known overlay marks. The first mark and/or thesecond mark may have the pitch of known marks, such as known alignmentmarks, and may be measurable using known measurement systems.

Using different types of mark mean that aberration related drifts andthe offsets between these marks can be corrected. If the staticprojection system aberration exists, the methods of the presentembodiment can measure this static offset using an alignment mark thefirst mark and another structure, such as an overlay mark or a productmark as the second mark. The static non-zero offsets can be minimizedusing the above described methods such that non-zero offsets will notneed to be calibrated. Different types of mark, such as alignment marks,overlay marks and product features or the like may have differentpitches. Therefore, it may be difficult of impossible to match thedifferent types of mark such that they overlap but do not touch. In thepresent embodiment, the methods described above should allow for thisusing measurements and corrections for the differences in pitch.

One of the advantages of the present embodiment is that dense samplingis not required to obtain the necessary relative shift described above.Therefore, the measurements can be carried out using systems already inplace as described above, i.e. metrology systems which are alreadyintegrated in the litho tool 100. Furthermore, this means that it is notnecessary to have a large number of marks. The layer comprising thefirst mark may comprise any number of suitable first marks. The layercomprising the second mark may comprise any number of suitable secondmarks. Preferably, there are the same number of first marks and secondmarks. For example, the layer comprising the first mark may comprises atleast five to ten first marks and the layer comprising the second markmay comprise a corresponding number of second marks, i.e. the samenumber of second marks. In other words, there may be the same number offirst marks and second marks on the relevant layers. The projectionsystem induced error is generally a translation error in case ofstandard inter field wafer alignment whose layout is one mark per fieldwith many fields, which means that a small number of marks, e.g. five toten, may be sufficient. Furthermore, linear and higher order parametererrors can be taken into account by using additional marks in a field.Thus, there can be more than ten first marks and more than ten secondmarks on the relevant layer(s).

The methods described in the second embodiment may be used to determinethe relative shift and/or the projection system induced error asdescribed above. As already indicated, the projection system inducederror can be an issue when any marks are created on the layer of thesubstrate. Thus, when determining the updated position for the featureusing the methods of the first embodiment, determining the updatedposition for the feature may use the relative shift and/or theprojection system induced error determined in the methods described inrelation to the second embodiment.

In a regular second-to-first layer overlay measurement there is a bottomgrating which is printed during the first layer exposure, and there is atop grating which is printed during the second layer exposure. In thesecond embodiment described above, the first mark and the second markare provided on one layer. The one layer may be the first layer. Thismeans that the relative responses of different pattern structures due toprojection system heating can be measured after they are printed (i.e.exposed).

In the second embodiment, there is provided a further method forcontrolling positioning of a substrate. The further method may have allof the same features as described in the second embodiment and comprisesproviding a substrate with a first mark on a first layer and a secondmark on a second layer of the substrate. In the further method, thesecond mark is the equivalent of the first mark and the second markdescribed above. Thus, in the further method, the second mark comprisesat least two types of feature. Thus, the second mark comprises at leastone first portion and at least one second portion as described above. Inthe further method, the at least one first portion corresponds to thefirst mark described above and the at least one second portioncorresponds to the second mark described above, and the first mark ofthe further method corresponds to an additional mark (i.e. the thirdmark in the context of the method already described). The further methodmay further comprise determining the position of the first mark anddetermining a relative shift of the at least one first portion withrespect to the at least one second portion. The method comprisescontrolling positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate based on the determinedposition and a determined relative shift. The further method differsfrom the previously described method due to the inclusion of the firstmark (which corresponds to the third mark in the method describedabove). Furthermore, there may be different numbers of first mark andsecond mark in the further method.

Using this further method, the positioning of the first layer or afurther layer of the substrate or any layer on a further substrate canbe controlled based on the position of the first mark and the relativeshift of the at least one first portion with respect to the at least onesecond portion. The relative shift of the at least one first portionwith respect to the at least one second portion can be described as acharacteristic of the second mark. Similarly to the method describedabove, the relative shift of the at least one first portion with respectto the at least one second portion can be used to determine a projectionsystem induced error and the projection system induced error can be usedto control positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate. The relative shift of theat least one first portion with respect to the at least one secondportion can be determined in the same way as described above withrespect to the first mark and the second mark above, i.e. using positionmeasurements and/or diffraction based measurements.

In the second embodiment, a substrate is provided with the first markand the second mark on the relevant layers. For example the first markis provided to a first layer and the second marker is provided to asecond layer on the substrate. However, the method may further comprisea step of exposing the first mark and/or the second mark on therespective layers of the substrate. This step is not necessary withinthe context of one or more embodiments of the invention because asubstrate already comprising these marks can be provided but the firstmark and/or the second mark can be made on the relevant layers of thesubstrate using the lithographic tool 100 described above.

The present embodiment described in the above method and further methodprovides many advantages. For example, using the projection systeminduced error as described above may reduce overlay error and thusimprove yield of the lithographic process. As described, static ordynamic offsets between a substrate alignment mark and product cell maybe reduced or removed. As described, using the method of the secondembodiment, the determined marker position may be corrected by thedetermined relative shift (which is based on measurements purely inresist; eg before processing takes place). As previously mentioned,etching and other processing may degrade the printed marker. Thus, nomark asymmetry is expected and measurement before such processing stepsmay be more accurate. Therefore the accuracy and precision may be higherthan measuring etched mark with mark asymmetry. The methods of thesecond embodiment will improve the correction which can be applied foreach substrate for a known drift using substrate level control. Thismeans that the correction (for the projection system induced error) maybe substrate specific; eg a relative shift may be measured for substrateA and a correction may be determined and applied specifically for a nextlayer on the same substrate A; hence corrections are finer than just lotbased corrections which typically apply to 25 substrates at once.

The present embodiment relaxes the substrate alignment mark design rulesto optimize aberration sensitivity. Thus, it is not necessary to useexpensive experimental determination of sensitivities for mark designbecause this can be avoided. Additionally, there is more freedom tochoose active alignment marks because the projection system inducederror can be accounted for, thus, there is no need (or a reduced need)to consider aberration sensitivity when selecting an alignment mark.Furthermore, no additional (e.g. alignment) marker measurements areneeded in order to correct for projection system induced errors. Thefirst mark and the second mark can be measured prior to the top layerexposure, e.g. just after resist development (this is bottom layerexposure) and thus the relative shift can be determined. During the toplayer exposure, there may be additional substrate alignment measurements(only standard substrate alignment). Thus, the stored relative shift canbe fed back per wafer to the top layer exposure. Hence there is nothroughput impact during the exposure and also the relative shift iscollected at the top layer exposure.

In an embodiment, a system is provided comprising a processor configuredto determine a position of a feature referenced to a substrate and/orcontrol positioning of a substrate. The processor is configured to carryout the method according to any one of the embodiments above. Theprocessor may be part of, or connected to, either the automated processcontrol (APC) system and/or the supervisory control system.

The processor may be configured to: measure a position of the feature,wherein the feature is configured to enable positioning of thesubstrate; receive an intended placement of the feature; determine anestimate of a placement error, wherein the placement error is thedifference between the intended placement and an actual placement of thefeature, based on knowledge of a relative position of a first featurereferenced to a first layer with respect to a second feature referencedto a second layer, wherein the first layer and the second layer are on asubstrate; and determine an updated position for the feature using theestimate of the placement error and the measured position of thefeature.

The processor may be configured to determine a relative shift of a firstmark with respect to a second mark, wherein the first mark and thesecond mark are on one layer of a substrate, wherein the first mark isdifferent from the second mark; and control positioning of a furtherlayer of the substrate or a layer of a further substrate based on therelative shift.

The processor may be configured to provide a substrate with a first markon a first layer and a second mark on a second layer of the substrate,the second mark comprising at least one first portion and at least onesecond portion; determine the position of the first mark; determine arelative shift of the at least one first portion with respect to the atleast one second portion; and use the determined position and determinedrelative shift to control positioning of the first layer or a furtherlayer of the substrate or any layer on a further substrate.

The above methods may be implemented using a computer program containingone or more sequences of machine-readable instructions describingmethods of combining process model values and measurement values asdescribed above. There may also be provided a data storage medium (e.g.,semiconductor memory, magnetic or optical disk) having such a computerprogram stored therein.

In an embodiment, a program is provided for controlling determining aposition of a feature referenced to a substrate and/or controllingpositioning of a substrate. The program may comprise instructions forcarrying out the steps of any of the methods described above.

The program may comprise instructions for carrying out the steps of:measuring a position of the feature, wherein the feature is configuredto enable positioning of the substrate; receiving an intended placementof the feature; determining an estimate of a placement error, whereinthe placement error is the difference between the intended placement andan actual placement of the feature, based on knowledge of a relativeposition of a first feature referenced to a first layer with respect toa second feature referenced to a second layer, wherein the first layerand the second layer are on a substrate; and determining an updatedposition for the feature using the estimate of the placement error andthe measured position of the feature.

The program may comprise instructions for carrying out the steps of:determining a relative shift of a first mark with respect to a secondmark, wherein the first mark and the second mark are on one layer of asubstrate, wherein the first mark is different from the second mark; andcontrolling positioning of a further layer of the substrate or a layerof a further substrate based on the relative shift.

The program may comprise instructions for carrying out the steps of:providing a substrate with a first mark on a first layer and a secondmark on a second layer of the substrate, the second mark comprising atleast one first portion and at least one second portion; determining theposition of the first mark; determining a relative shift of the at leastone first portion with respect to the at least one second portion; andusing the determined position and determined relative shift to controlpositioning of the first layer or a further layer of the substrate orany layer on a further substrate. The computer program may be executedfor example within the control unit LACU of FIG. 1, or some othercontroller, for example within a metrology system that includes themetrology apparatus 140, or in an advanced process control system orseparate advisory tool. The program may optionally be stored in a memorywhich is part of or can be accessed by the automated process control(APC) system and/or the supervisory control system.

Further embodiments of the invention are disclosed in the list ofnumbered embodiments below:

1. A method for determining a position of a feature referenced to asubstrate, the method comprising:

measuring a position of the feature, wherein the feature is configuredto enable positioning of the substrate;

receiving an intended placement of the feature;

determining an estimate of a placement error, wherein the placementerror is the difference between the intended placement and an actualplacement of the feature, based on knowledge of a relative position of afirst reference feature referenced to a first layer with respect to asecond reference feature referenced to a second layer, wherein the firstlayer and the second layer are on a substrate; and determining anupdated position for the feature using the estimate of the placementerror and the measured position of the feature.

2. The method of embodiment 1, further comprising positioning asubstrate on the basis of the updated position of the feature.

3. The method of embodiment 2 further comprising a step of exposing thesubstrate to a radiation beam.

4. The method of embodiment 2 or 3, wherein the method is carried outusing a lithographic apparatus.

5. The method of any of the preceding embodiments, wherein the featureis on the first layer or on the second layer.

6. The method of any of the preceding embodiments, wherein the featureis on a layer of a substrate having the first layer and the secondlayer, and the feature is on a different layer than the first layer andthe second layer.

7. The method of any of the preceding embodiments, wherein the positionof the feature is measured on a substrate different from the substrateassociated with the determined estimate of the placement error.

8. The method of any of the preceding embodiments, wherein the methodfurther comprises measuring the position of a first reference featurerelative to the position of a second reference feature to determine anoverlay error and using the overlay error to determine the estimate ofthe placement error.9. The method of any of the preceding embodiments, wherein the methodfurther comprises modelling an overlay error between the first layer andthe second layer to determine the position of the first referencefeature relative to the position of the second reference feature.10. The method of embodiment 9, further comprising receiving contextinformation and/or lithographic apparatus information, and using thecontext information and/or lithographic apparatus information to modelthe overlay error, wherein the context information and/or lithographicapparatus relates to measured and/or modelled deformation of at leastone of the substrate, a patterning device and/or a projection system.11. The method of embodiment 9 or 10, wherein modelling the overlayerror comprises using a predetermined value based on overlay data.12. The method of any one of embodiments 8 to 11, wherein the estimateof the placement error is determined to be the same as the overlayerror.13. The method of any one of the preceding embodiments, wherein thefeature is a grating and/or an alignment mark.14. A system comprising a processor configured to determine a positionof a feature referenced to a substrate, the processor being configuredto:

measure a position of the feature, wherein the feature is configured toenable positioning of the substrate;

receive an intended placement of the feature;

determine an estimate of a placement error, wherein the placement erroris the difference between the intended placement and an actual placementof the feature, based on knowledge of a relative position of a firstreference feature referenced to a first layer with respect to a secondreference feature referenced to a second layer, wherein the first layerand the second layer are on a substrate; and

determine an updated position for the feature using the estimate of theplacement error and the measured position of the feature.

15. A program for controlling determining a position of a featurereferenced to a substrate, the program comprising instructions forcarrying out the steps of:

measuring a position of the feature, wherein the feature is configuredto enable positioning of the substrate;

receiving an intended placement of the feature;

determining an estimate of a placement error, wherein the placementerror is the difference between the intended placement and an actualplacement of the feature, based on knowledge of a relative position of afirst reference feature referenced to a first layer with respect to asecond reference feature referenced to a second layer, wherein the firstlayer and the second layer are on a substrate; and determining anupdated position for the feature using the estimate of the placementerror and the measured position of the feature.

16. A method for controlling positioning of a substrate, comprising:

providing a substrate with a first mark and a second mark on one layerof the substrate, wherein the first mark is different from the secondmark;

determining a relative shift of the first mark with respect to thesecond mark; and

controlling positioning of the one layer of the substrate, a furtherlayer of the substrate or a layer of a further substrate based on thedetermined relative shift.

17. The method of embodiment 16, wherein the first mark and the secondmark have different sensitivities to an aberration in a projectionsystem, wherein the projection system is used to expose the first markand the second mark on the substrate.

18. The method of embodiment 16 or 17, further comprising determining aprojection system induced error using the determined relative shift andthe controlling positioning of the one layer of the substrate, a furtherlayer of the substrate or a layer of a further substrate uses thedetermined projection system induced error.19. The method of any one of embodiments 16-18, further comprisingmeasuring the position of the first mark and the second mark andcalculating the distance between the first mark and the second mark, andwherein the relative shift is determined using the calculated distancebetween the first mark and the second mark and an expected distancebetween the first mark and the second mark.20. The method of any one of embodiment 16-18, wherein the relativeshift is determined using a diffraction based measurement.21. The method of any one of embodiments 16-20, wherein the determinedrelative shift is used in a feedback loop to control positioning of alayer of a further substrate and/or in a feedforward loop to controlpositioning of a further layer of the same substrate.22. The method of any one of embodiments 16-21, wherein the first markis an alignment mark or an overlay mark, and wherein the second mark isa product feature or a feature having a similar response to theprojection system induced error as a product feature.23. The method of any one of embodiments 16-22, wherein the layercomprising the first mark comprises at least five to ten first marks andthe layer comprising the second mark comprises the same number of secondmarks.24. The method of any one of embodiments 16-23, wherein the first markand the second mark overlap.25. The method of any one of embodiments 16-24, wherein the first markhas multiple first portions and the second mark has multiple secondportions.26. A method for controlling positioning of a substrate, comprising:

providing a substrate with a first mark on a first layer and a secondmark on a second layer of the substrate, the second mark comprising atleast one first portion and at least one second portion;

determining the position of the first mark;

determining a relative shift of the at least one first portion withrespect to the at least one second portion; and

controlling positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate based on the determinedposition and the determined relative shift.

27. The method of embodiment 26, wherein the at least one first portionand the at least one second portion have different sensitivities to anaberration in a projection system, wherein the projection system is usedto expose the second mark.

28. The method of embodiment 26 or 27, wherein the relative shift isdetermined by measuring of a position of the at least one first portionand a position of the at least one second portion and/or using adiffraction based measurement.

29. The method of any one of embodiments 26-28, wherein the first markhas multiple first portions and the second mark has multiple secondportions.

30. The method of any one of embodiments 29, wherein the first portionsand the second portions are interlaced.

31. The method of any one of embodiments 26 to 30, wherein a firstportion comprises fewer elements than a second portion.

32. The method of any one of embodiments 26-31, wherein a first portioncomprises only a single element.

33. The method of any one of embodiments 26-32, wherein a single elementof a first portion is larger than a single element of a second portion.

34. The method of any one of embodiments 26-33, wherein at least one ofthe second portions comprises a plurality of elements.

35. The method of embodiment 34, wherein the pitch between the secondportions is larger than the pitch between the plurality of elements ofthe second portion.

36. The method of embodiment 34 or 35, wherein a single element of afirst portion corresponds in size to the plurality of elements making upa second portion.

37. The method of any one of embodiments 26 and 29-36, wherein the firstportions are substantially consistent in shape and pitch, and the secondportions are substantially consistent in shape and pitch.

38. The method of any one of embodiments 26-36, wherein the determinedposition and the relative shift are used to determine a projectionsystem induced error and the projection system induced error is used tocontrol positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate.39. The method of any one of embodiments 18-25 or 38, wherein thedetermined projection system induced error is due to projection systemdrift and/or projection system heating.40. The method of any one of embodiments 18-25, 38 or 39, wherein thedetermined projection system induced error is used in a feedback loop tocontrol positioning of a layer of a further substrate and/or in afeedforward loop to control positioning of a further layer of the samesubstrate.41. The method of any one of embodiments 16-40, further comprisingexposing the first mark and the second mark on the respective layer ofthe substrate.42. The method of any one of embodiments 1 to 13, wherein determiningthe updated position for the feature uses the relative shift and/or theprojection system induced error determined in any one of embodiments 16to 41.43. A system comprising a processor configured to control positioning ofa substrate, the processor being configured to:

determine a relative shift of a first mark with respect to a secondmark, wherein the first mark and the second mark are on one layer of asubstrate, wherein the first mark is different from the second mark; andcontrol positioning of a further layer of the substrate or a layer of afurther substrate using the determined relative shift.

44. A program for controlling positioning of a substrate, the programcomprising instructions for carrying out the steps of:

determining a relative shift of a first mark with respect to a secondmark, wherein the first mark and the second mark are on one layer of asubstrate, wherein the first mark is different from the second mark; andcontrolling positioning of a further layer of the substrate or a layerof a further substrate using the determined relative shift.

45. A system comprising a processor configured to control positioning ofa substrate, the processor being configured to:

provide a substrate with a first mark on a first layer and a second markon a second layer of the substrate, the second mark comprising at leastone first portion and at least one second portion;

determine the position of the first mark;

determine a relative shift of the at least one first portion withrespect to the at least one second portion; and

use the determined position and the determined relative shift to controlpositioning of the first layer or a further layer of the substrate orany layer on a further substrate.

46. A program for controlling positioning of a substrate, the programcomprising instructions for carrying out the steps of:

providing a substrate with a first mark on a first layer and a secondmark on a second layer of the substrate, the second mark comprising atleast one first portion and at least one second portion;

determining the position of the first mark;

determining a relative shift of the at least one first portion withrespect to the at least one second portion; and

using the determined position and the determined relative shift tocontrol positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate.

CONCLUSION

In conclusion, the present disclosure provides a method generating anupdated position for a feature referenced to a substrate, which can beused in various different ways. This allows the error introduced whenforming the feature to be reduced or negated by processing steps. Thepresent disclosure also provides a method for controlling positioning ofa substrate. This allows the effect of projection system induced errorto be reduced or prevented.

The disclosed methods allow the provision of a lithographic apparatusand methods of operating a lithographic apparatus in which performanceparameters such as overlay can be improved, without the need foradditional measurements, or even with a reduced number of measurements.The determination of the first reference feature and the secondreference feature can be performed with or without using additionalcontext information and/or lithographic apparatus information.Throughput can be maintained and/or increased, due to the increasedaccuracy which substrates (including those for which no measurement dataassociated with the first reference feature and the second referencefeature is available) can be positioned without the loss of performancethat might otherwise result.

The steps of combining determining an estimate of the placement errorand determining an updated position can be performed in any suitableprocessing apparatus, which may located anywhere in the facility of FIG.1, or may be physically remote from the facility. Steps of the methodmay be carried out in separate parts of the apparatus.

The updated position and/or estimated position error may be calculatedin the supervisory control system of FIG. 1, or in the litho toolcontrol unit LACU. They may be calculated in a remote system andcommunicated to the facility afterwards. Any model and measurement datamay be delivered separately to a processing apparatus which thencombines them as part of calculating the estimate of the position errorand/or the updated position.

The method and variations above are described as being carried out usinga lithographic apparatus. However, other apparatus may be used. Thepatterning step of a lithographic manufacturing process is only oneexample where the principles of the present disclosure may be applied.Other parts of the lithographic process, and other types ofmanufacturing process, may also benefit from the generation of modifiedestimates and corrections in the manner disclosed herein.

These and other modifications and variations can be envisaged by theskilled reader from a consideration of the present disclosure. Thebreadth and scope of the present invention should not be limited by anyof the above-described exemplary embodiments, but should be defined onlyin accordance with the following claims and their equivalents.

The invention claimed is:
 1. A method comprising: determining a relativeshift of a first mark with respect to a second mark, wherein a substratehas the first mark and the second mark on one layer of the substrate,wherein the first mark has multiple first portions and the second markhas multiple second portions, wherein the first portions and the secondportions are interlaced, wherein the first mark is different from thesecond mark, wherein the first mark and the second mark are exposedtogether in a same exposure in the one layer, and wherein the relativeshift is determined from measurement of the first and second marks whilein resist; and controlling, based on the determined relative shift,positioning of the one layer of the substrate, a further layer of thesubstrate or a layer of a further substrate.
 2. The method of claim 1,wherein the first mark and the second mark have different sensitivitiesto an aberration in a projection system, the projection system used toexpose the first mark and the second mark on the substrate.
 3. Themethod of claim 1, further comprising determining a projection systeminduced error using the determined relative shift and the controllingpositioning of the one layer of the substrate, a further layer of thesubstrate or a layer of a further substrate uses the determinedprojection system induced error.
 4. The method of claim 1, furthercomprising measuring a position of the first mark and the second markand calculating the distance between the first mark and the second mark,wherein the relative shift is determined using the calculated distancebetween the first mark and the second mark and an expected distancebetween the first mark and the second mark.
 5. The method of claim 1,wherein the relative shift is determined using a diffraction basedmeasurement.
 6. The method of claim 1, wherein the determined relativeshift is used in a feedback loop to control positioning of a layer of afurther substrate and/or in a feedforward loop to control positioning ofa further layer of the same substrate.
 7. The method of claim 1, whereinthe first mark is an alignment mark or an overlay mark, and wherein thesecond mark is a product feature or a feature having a similar responseto a projection system induced error as a product feature.
 8. The methodof claim 1, wherein the layer comprising the first mark comprises atleast five to ten first marks and the layer comprising the second markcomprises the same number of second marks.
 9. A computer program productcomprising a non-transitory computer-readable medium having instructionstherein, the instruction, upon execution by a computer system,configured to cause the computer system to at least: determine arelative shift of a first mark with respect to a second mark, wherein asubstrate has the first mark and the second mark on one layer of thesubstrate, wherein the first mark has multiple first portions and thesecond mark has multiple second portions, wherein the first portions andthe second portions are interlaced, wherein the first mark is differentfrom the second mark, wherein the first mark and the second mark areexposed together in a same exposure in the one layer, and wherein therelative shift is determined from measurement of the first and secondmarks while in resist; and control, based on the determined relativeshift, positioning of the one layer of the substrate, a further layer ofthe substrate or a layer of a further substrate.
 10. The computerprogram product of claim 9, wherein the first mark and the second markhave different sensitivities to an aberration in a projection system,the projection system used to expose the first mark and the second markon the substrate.
 11. The computer program product of claim 9, whereinthe first mark is an alignment mark or an overlay mark, and wherein thesecond mark is a product feature or a feature having a similar responseto a projection system induced error as a product feature.
 12. A methodcomprising: determining a position of a first mark, wherein a substratehas the first mark on a first layer of the substrate and a second markon a second layer of the substrate, wherein the second mark has multiplefirst portions and multiple second portions, wherein the first andsecond portions are interlaced, wherein at least one first portion andat least one second portion are exposed together in a same exposure inthe second layer; determining a relative shift of the at least one firstportion with respect to the at least one second portion, wherein therelative shift is determined from measurement of the at least one firstportion and the at least one second portion while in resist; andcontrolling, based on the determined position and the determinedrelative shift, positioning of the first layer or a further layer of thesubstrate or any layer on a further substrate.
 13. The method of claim12, wherein the at least one first portion and the at least one secondportion have different sensitivities to an aberration in a projectionsystem, the projection system used to expose the second mark.
 14. Themethod of claim 12, wherein the relative shift is determined bymeasuring of a position of the at least one first portion and a positionof the at least one second portion and/or using a diffraction basedmeasurement.
 15. The method of claim 12, wherein the first portions aresubstantially consistent in shape and pitch, and the second portions aresubstantially consistent in shape and pitch.
 16. The method of claim 12,wherein a first portion comprises fewer elements than a second portion.17. The method of claim 12, wherein a first portion comprises only asingle element.
 18. The method of claim 12, wherein a single element ofa first portion is larger than a single element of a second portion. 19.The method of claim 12, wherein at least one second portion of the atleast one second portion comprises a plurality of elements.
 20. Themethod of claim 19, wherein a pitch between a plurality of secondportions is larger than a pitch between the plurality of elements of theat least one second portion.
 21. The method of claim 19, wherein asingle element of a first portion corresponds in size to the pluralityof elements making up at least one second portion.
 22. The method ofclaim 12, wherein the determined position and the relative shift areused to determine a projection system induced error and the projectionsystem induced error is used to control positioning of the first layeror a further layer of the substrate or any layer on a further substrate.23. The method of claim 22, wherein the determined projection systeminduced error is used in a feedback loop to control positioning of alayer of a further substrate and/or in a feedforward loop to controlpositioning of a further layer of the same substrate.
 24. A computerprogram product comprising a non-transitory computer-readable mediumhaving instructions therein, the instruction, upon execution by acomputer system, configured to cause the computer system to at least:determine a position of a first mark, wherein a substrate has the firstmark on a first layer of the substrate and a second mark on a secondlayer of the substrate, wherein the second mark has multiple firstportions and multiple second portions, wherein the first and secondportions are interlaced, wherein at least one first portion and at leastone second portion are exposed together in a same exposure in the secondlayer; determine a relative shift of the at least one first portion withrespect to the at least one second portion, wherein the relative shiftis determined from measurement of the at least one first portion and theat least one second portion while in resist; and control, based on thedetermined position and the determined relative shift, positioning ofthe first layer or a further layer of the substrate or any layer on afurther substrate.
 25. The computer program product of claim 24, whereinthe at least one first portion and the at least one second portion havedifferent sensitivities to an aberration in a projection system, theprojection system used to expose the second mark.
 26. The computerprogram product of claim 24, wherein the relative shift is determined bymeasurement of a position of the at least one first portion and aposition of the at least one second portion and/or by use of adiffraction based measurement.